Conventionally known is a distributed control system including a host control device, local control devices, and an integrated control device (for example, refer to Patent Literature 1). In this distributed control system, the host control device monitors and controls an overall plant, the local control devices control individual units in the plant, and the integrated control device integrates and controls the local control devices by function. The host control device includes a plant control means having an equal function to that of a plant control means of the integrated control device so as to perform plant control instead of the integrated control device at the time of occurrence of a failure of the integrated control device.